An improvement in ignitability is required for spark plugs in order to improve fuel consumption and reduce the amount of imperfect combustion gases. In the related spark plugs under such requirement, noble metals are used for a center electrode and a ground electrode. In addition, in these related spark plugs, that the ground electrode has a narrow width portion to improve the ignitability (for example, Patent Document 1).
However, it has generally been desired a technology to improve the ignitability without using any expensive noble metal materials.